The present invention relates generally to material handling devices and more particularly to an improved boom and dipper stick construction for mobile excavators and an improved method of manufacturing the same.
One type of known material handling device, which has been in existence for some time, includes a boom carried by a support for pivotal movement in a substantially vertical plane about a horizontal axis. The boom is generally pivoted on the support by a fluid power means while the support is rotatable about a vertical axis on a self-powered frame.
The free end of the boom pivotally supports a material handling unit, such as a dipper stick having a bucket pivoted thereon. The dipper stick is pivoted relative to the free end of the boom through additional fluid power means while the bucket is pivoted on the dipper stick through a further fluid power means. Devices of this general character are shown in Przybylski U.S. Pat. No. 3,392,855 and Davis U.S. Pat. No. 2,961,106.
The boom and dipper stick are typically fabricated by welding together numerous specifically formed steel plates to form generally box-type structures. The various hinge points are provided with suitble bearings and connecting means welded to the plates. It has heretofore been necessary to provide doubler plates on the side of the structures in the areas of high stress concentrations.